JP6667982B2 - Flexible wiring board - Google Patents

Description

  The present invention relates to a flexible wiring board in which a part of a copper layer constituting a wiring is deposited by a copper electroplating method to improve folding resistance.

  2. Description of the Related Art Flexible wiring boards are widely used for parts requiring bending or bending of electronic devices, such as hard disk read / write heads and printer heads, and bending wiring of IC packages mounted with driver ICs for liquid crystal displays, utilizing their flexibility. . In particular, in an IC package of a liquid crystal display, the liquid crystal display is bent and mounted from an end on a front surface side (a side on which an image is displayed) of the liquid crystal display to a rear surface side of the liquid crystal display.

  In order to manufacture such a flexible wiring board, a flexible wiring board (flexible copper clad laminate, also called FCCL), in which a copper layer and a resin layer are laminated, is wired using a subtractive method or a semi-additive method. A processing method is used.

The subtractive method is generally a method of chemically etching a copper layer of a copper-clad laminate to remove unnecessary portions.
That is, a resist is provided on the surface of a portion of the copper layer of the flexible wiring board that is to be left as a conductor wiring, and the unnecessary portion of the copper layer is selectively removed through a chemical etching process using an etching solution corresponding to copper and washing with water. To form conductor wiring.

On the other hand, with the semi-additive method, a resist layer is formed on the base metal layer and ultra-thin copper layer of the copper clad laminate, the resist layer is patterned by photolithography, and the resist layer where wiring is to be formed is removed. Copper plating is applied to the opening where the ultra-thin copper layer obtained is exposed to form a wiring. After the wiring is formed, the resist is removed, and the ultra-thin copper layer and the underlying metal layer are chemically etched to remove the ultra-thin copper layer and the underlying metal layer.
That is, without forming a resist on the surface of the portion of the copper layer of the flexible wiring substrate where the conductor wiring is desired to be formed, copper is deposited by an electrolytic copper plating method, and an etching solution corresponding to the ultra-thin copper layer and the base metal layer is used. Through chemical etching and washing, unnecessary portions of the ultra-thin copper layer and the underlying metal layer are selectively removed to form conductor wiring.

The flexible wiring board (FCCL) can be classified into a three-layer flexible wiring board (hereinafter, referred to as a three-layer FCCL) and a two-layer flexible wiring board (hereinafter, referred to as a two-layer FCCL).
The three-layer FCCL has a structure (copper foil / adhesive layer / resin film) in which an electrolytic copper foil or a rolled copper foil is adhered to a base (insulating layer) resin film. On the other hand, the two-layer FCCL has a structure (copper layer or copper foil / resin film) in which a copper layer or copper foil and a resin film substrate are laminated.

The above two-layer FCCL is roughly classified into three types.
FCCL (commonly called metallized substrate) formed by sequentially plating a base metal layer and a copper layer on the surface of a resin film, FCCL (commonly called cast substrate) formed by coating a varnish of a resin film on a copper foil and forming an insulating layer, And FCCL (commonly known as a laminate substrate) in which a resin film is laminated on a copper foil.

Among them, a metallized substrate, that is, an FCCL formed by sequentially plating a base metal layer and a copper layer on the surface of a resin film, the copper layer can be made thinner, and the smoothness of the polyimide film-copper layer interface is high. Therefore, as compared with a cast substrate, a laminated substrate, or a three-layer FCCL, it is more suitable for fine patterning of wiring.
For example, the thickness of a copper layer of a metallized substrate can be freely controlled by a dry plating method and an electroplating method, while the thickness of a cast substrate, a laminated substrate, or a three-layer FCCL is limited by the copper foil used. It is because it is done.

On the other hand, copper foil used for wiring of a flexible wiring board is resistant to refraction by, for example, a method of performing heat treatment on the copper foil (see Patent Document 1) or a method of performing rolling (see Patent Document 2). The performance is improved.
However, these methods relate to the treatment of the copper foil itself used for the cast substrate and the laminate substrate of the three-layer FCCL rolled copper foil, the electrolytic copper foil, and the two-layer FCCL.

For evaluation of the refraction resistance of the copper foil, a MIT refraction resistance test (Folding Endurance Test) standardized by “JIS C-5016-1994” or the like or “ASTM D2176” is used industrially. .
In this test, the evaluation is made based on the number of refractions until the circuit pattern formed on the test piece is broken, and it is considered that the larger the number of refractions, the better the refraction resistance.

JP-A-8-283886 JP-A-6-269807

The two-layer flexible wiring board to which the present invention is directed is a meta-layer in which a metal layer including a base metal layer, a copper thin film layer, and a copper electroplating layer is formed on at least one side of a resin film substrate without using an adhesive. Since it is a rising substrate, it is difficult to improve the bending resistance by subjecting only the copper plating layer to heat treatment or rolling as disclosed in the prior art document. Therefore, there has been a demand for a metallized substrate having improved bend resistance and improved bend resistance of the metallized substrate itself.
In view of such circumstances, the present invention provides a two-layer flexible wiring board excellent in breaking resistance and a method for manufacturing the same.

  In order to solve the above problems, the present inventors have conducted intensive studies on the breaking resistance of a copper layer formed on a polyimide resin layer by a plating method, and found that a change in crystal orientation before and after the breaking resistance was a bending resistance test. The effects on the results were confirmed, and the present invention was reached.

The first invention of the present invention is directed to a metal laminate comprising a base metal layer made of a nickel alloy on a surface of a resin film substrate without an adhesive, and a copper layer provided on the surface of the base metal layer. In the flexible wiring board provided with the wiring, the wiring of the metal laminate is [(200) / (200) /] of the crystal orientation ratio of the copper layer obtained before and after the “breaking resistance test specified in JIS C-5016-1994”. (111)] An electron beam having an orientation ratio difference d [(200) / (111)] of not less than 0.03 and a film thickness range from the surface of the resin film substrate to 0.4 μm of the metal laminate. the ratio of the crystal fraction _{OR 111} of 111 orientation with respect to the crystal fraction _{OR 001} 001 orientation of the measured crystal _(OR 111 _{/ OR 001)} is 7 or less backscatter diffraction (EBSD), Contact in the width direction of the wiring A bottom width B and a top width T of the cross-sectional shape that a central portion width M substantially in the center of the bottom and top has a relationship of the following equation (1), and is at 50μm or less bottom width B, wherein the bottom width B The flexible wiring board is characterized in that the width M of the central portion, the width T of the top portion, and the thickness of the copper layer have a relationship represented by the following equation (2).

  According to a second aspect of the present invention, there is provided a flexible wiring board according to the first aspect, wherein the thickness of the base metal layer is 3 nm to 50 nm.

  A third aspect of the present invention is a flexible wiring board, wherein the thickness of the copper layer in the first and second aspects is 5 μm to 12 μm.

  In a fourth aspect of the present invention, the resin film substrate according to the first to third aspects is characterized in that a polyimide-based film, a polyamide-based film, a polyester-based film, a polytetrafluoroethylene-based film, a polyphenylene sulfide-based film, a polyethylene naphthalate-based film A flexible wiring board comprising at least one resin film selected from a film and a liquid crystal polymer film.

  A metal laminate, which is a wiring formed by laminating a base metal layer and a copper layer without using an adhesive, is provided on the surface of the resin film substrate, and is subjected to a bending resistance test (withstand resistance specified in “JIS C-5016-1994”). The present invention in which the difference d [(200) / (111)] in the [(200) / (111)] orientation ratio of the crystal orientation of the copper layer obtained before and after the execution of the folding test) is 0.03 or more. According to the flexible wiring board of the above, the breaking resistance of the substrate is remarkably improved, and an industrially remarkable effect is achieved.

  In particular, the flexible wiring board according to the present invention, which is excellent in fold resistance, can be bent with a smaller radius than conventional products, and can be bent with a small radius when used for a driver IC package of a liquid crystal display. Therefore, the protrusion of the IC package that bends around the liquid crystal display from the liquid crystal display can be reduced, and has a design effect of reducing the size of the housing of the liquid crystal display.

FIG. 2 is a schematic cross-sectional view of a two-layer flexible wiring substrate manufactured by a metallizing method used in the present invention. 1 is a schematic diagram showing a roll-to-roll sputtering apparatus for forming a base metal layer and a copper thin film layer of a two-layer flexible wiring board used for a flexible wiring board of the present invention. FIG. 3 is a schematic view showing a roll-to-roll continuous plating apparatus for performing electroplating in the production of a two-layer flexible wiring board used for the flexible wiring board of the present invention. It is the figure which showed typically the time and current density of PR current in this invention.

  The flexible wiring board according to the present invention is obtained by wiring a two-layer flexible wiring substrate by a subtractive method or a semi-additive method.

  Therefore, the present invention will be described using a flexible wiring board according to the present invention, which is manufactured by performing wiring processing on a two-layer flexible wiring substrate using a subtractive method. The manufacturing method is not limited as long as the crystal structure of the flexible wiring board according to the present invention and the cross-sectional shape of the wiring can be achieved.

(1) Two-layer flexible wiring board First, the two-layer flexible wiring board used for the flexible wiring board of the present invention will be described.
The two-layer flexible wiring board used in the present invention is a metal laminate having a laminated structure in which a base metal layer and a copper layer are sequentially laminated on at least one surface of a resin film substrate such as a polyimide film without using an adhesive. And the copper layer is constituted by a copper thin film layer and a copper electroplating layer.

FIG. 1 is a schematic view showing a cross section of a two-layer flexible wiring board 6 manufactured by a metallizing method, and is also a cross-sectional view of a wiring portion in a flexible wiring board according to the present invention.
A polyimide film is used for the resin film substrate 1, and on at least one surface of the polyimide film 1, a base metal layer 2, a copper thin film layer 3, and a copper electroplating layer 4 are formed and laminated in this order from the polyimide film 1 side. I have. The copper thin film layer 3 and the copper electroplating layer 4 constitute a copper layer 5, and a metal laminate 7 including the copper layer 5 and the base metal layer 2 is formed.

As the resin film substrate 1 to be used, besides a polyimide film, a polyamide film, a polyester film, a polytetrafluoroethylene film, a polyphenylene sulfide film, a polyethylene naphthalate film, a liquid crystal polymer film, or the like can be used.
In particular, a polyimide film is particularly preferable from the viewpoint of mechanical strength, heat resistance, and electrical insulation.
Further, the resin film substrate having a film thickness of 12.5 to 75 μm can be preferably used.

  The base metal layer 2 ensures reliability such as adhesion between the resin film substrate and a metal layer such as copper and heat resistance. Therefore, the material of the base metal layer is selected from nickel, chromium, and any one of these alloys. However, in consideration of the adhesion strength and the ease of etching at the time of manufacturing the wiring, the nickel-chromium alloy is used. Are suitable.

The composition of the nickel-chromium alloy is desirably 15% by weight or more and 22% by weight or less of chromium, and improvement in corrosion resistance and migration resistance can be expected.
Among them, a nickel-chromium alloy of 20% by weight of chromium is distributed as a nichrome alloy and can be easily obtained as a sputtering target of a magnetron sputtering method. Further, chromium, vanadium, titanium, molybdenum, cobalt, or the like may be added to the alloy containing nickel.
Further, a plurality of nickel-chromium alloy thin films having different chromium concentrations may be stacked to form a base metal layer having a nickel-chromium alloy concentration gradient.

The thickness of the base metal layer 2 is preferably 3 nm to 50 nm.
If the thickness of the underlying metal layer is less than 3 nm, the adhesion between the polyimide film and the copper layer cannot be maintained, and the corrosion resistance and migration resistance are inferior. On the other hand, if the thickness of the underlying metal layer exceeds 50 nm, it may be difficult to sufficiently remove the underlying metal layer when performing wiring processing by the subtractive method. If the removal of the underlying metal layer is insufficient, there is a concern that problems such as migration between wirings may occur.

The copper thin film layer 3 is mainly composed of copper, and its thickness is desirably 10 nm to 1 μm.
If the thickness of the copper thin film layer is less than 10 nm, conductivity cannot be ensured when the copper electroplating layer is formed on the copper thin film layer by the electroplating method, leading to poor appearance during electroplating. If the thickness of the copper thin film layer exceeds 1 μm, there is no problem in quality of the two-layer flexible wiring board, but there is a problem in that productivity is poor.

(2) Method of forming base metal layer and copper thin film layer The base metal layer and the copper thin film layer are preferably formed by dry plating.
Examples of the dry plating method include a sputtering method, an ion plating method, a cluster ion beam method, a vacuum deposition method, and a CVD method. In the dry plating method, a sputtering method is desirable from the viewpoint of controlling the composition of the seed layer and the like.

  For forming a film on the resin film substrate by sputtering, it is sufficient to form the film using a known sputtering device. In the case of a long resin film substrate, the film can be formed by a known roll-to-roll sputtering device. Using this roll-to-roll sputtering apparatus, a base metal layer and a copper thin film layer can be continuously formed on the surface of a long polyimide film.

FIG. 2 shows an example of a roll-to-roll sputtering apparatus used.
The roll-to-roll sputtering apparatus 10 includes a rectangular parallelepiped housing 12 that houses most of the components.
The housing 12 may be cylindrical and may have any shape, as long as it can maintain a reduced pressure in the range of 10 ⁻⁴ Pa to 1 Pa.
In the housing 12, an unwinding roll 13, a can roll 14, a sputtering cathode 15a, 15b, 15c, 15d, a front feed roll 16a, and a rear feed roll for supplying a polyimide film F which is a long resin film substrate. 16b, a tension roll 17a, a tension roll 17b, and a winding roll 18.

The unwinding roll 13, the can roll 14, the front feed roll 16a, and the winding roll 18 are provided with power by a servo motor. The unwind roll 13 and the take-up roll 18 maintain the tension balance of the polyimide film F by controlling the torque with a powder clutch or the like.
The surfaces of the tension rolls 17a and 17b are finished with hard chrome plating and have tension sensors.
The sputtering cathodes 15a to 15d are arranged facing the can roll 14 in a magnetron cathode system. The dimension of the sputtering cathodes 15a to 15d in the width direction of the polyimide film F may be wider than the width of the long resin film polyimide film F.

The polyimide film F is transported in the roll-to-roll sputtering apparatus 10 which is a roll-to-roll vacuum film forming apparatus, and is formed by the sputtering cathodes 15a to 15d facing the can roll 14, and is provided with a copper thin film layer. It is processed into a polyimide film F2.
The surface of the can roll 14 is finished with hard chrome plating, and a coolant or a warm medium supplied from the outside of the housing 12 circulates inside the can roll 14, and is adjusted to a substantially constant temperature.

When a base metal layer and a copper thin film layer are formed using the roll-to-roll sputtering apparatus 10, a target having the composition of the base metal layer is mounted on the sputtering cathode 15a, and a copper target is mounted on the sputtering cathodes 15b to 15d. After the inside of the apparatus in which the polyimide film is set on the unwinding roll 13 is evacuated, a sputtering gas such as argon is introduced to maintain the inside of the apparatus at about 1.3 Pa.
Further, after the base metal layer is formed by sputtering, a copper thin film layer may be formed by an evaporation method.

(3) Copper electroplating layer and film forming method The copper electroplating layer is formed by an electroplating method. The thickness of the copper electroplating layer is desirably 1 μm to 20 μm.
Here, the electroplating method used is copper electroplating in which electroplating is performed using an insoluble anode in a copper sulfate plating bath containing iron ions, and the composition of the copper plating bath used is a commonly used flexible plating method. A high-slow copper sulfate plating bath used for through-hole plating of wiring boards may be used.

FIG. 3 shows an example of a roll-to-roll continuous electroplating apparatus (hereinafter, referred to as a plating apparatus 20) that can be used for manufacturing a two-layer flexible wiring board used for the flexible wiring board of the present invention.
The polyimide film F2 with the copper thin film layer obtained by forming the base metal layer and the copper thin film layer is unwound from the unwinding roll 22 and continuously immersed in the plating solution 28 in the electroplating tank 21 while repeating the immersion. Transported to 28a indicates the level of the plating solution.
The polyimide film F2 with a copper thin film layer is formed by depositing a copper layer on the surface of a metal thin film by electroplating while being immersed in the plating solution 28, forming a copper layer having a predetermined thickness, and then forming a metallized resin. The substrate is wound on a winding roll 29 as a two-layer flexible wiring substrate S which is a film substrate. In addition, the conveyance speed of the polyimide film F2 with a copper thin film layer is preferably in the range of several m to several tens m / min.

Specifically, the polyimide film F2 with a copper thin film layer is unwound from the unwinding roll 22, immersed in the plating solution 28 in the electroplating tank 21 via the power feeding roll 26a. The transport direction of the polyimide film F2 with a copper thin film layer that has entered the electroplating tank 21 is reversed through the reversing roll 23, and is drawn out of the electroplating tank 21 by the power supply roll 26b.
As described above, the copper film is formed on the metal thin film of the polyimide film F2 with the copper thin film layer while the immersion in the plating solution is repeated a plurality of times (10 times in FIG. 3). It is.

A power supply (not shown) is connected between the power supply roll 26a and the anode 24a.
An electroplating circuit is formed by the power supply roll 26a, the anode 24a, the plating solution, the polyimide film F2 with a copper thin film layer, and the power supply.
Here, the anode to be used is preferably an insoluble anode, and may be a known insoluble anode whose surface is coated with a conductive ceramic without requiring a special insoluble anode. A mechanism for supplying copper ions to the plating solution 28 is provided outside the electroplating tank 21.

  Copper ions are supplied to the plating solution 28 with an aqueous copper oxide solution, an aqueous copper hydroxide solution, an aqueous copper carbonate solution, or the like. Alternatively, there is a method in which a trace amount of iron ions are added to a plating solution to dissolve oxygen-free copper balls and supply copper ions. Any of the above methods can be used for supplying copper.

As for the current density during plating, the current density is increased stepwise as it proceeds downstream from the anode 24a in the transport direction, so that the maximum current density is obtained from the anodes 24o to 24t.
By increasing the current density in this way, discoloration of the copper layer can be prevented. In particular, when the current density is high when the thickness of the copper layer is small, discoloration of the copper layer is likely to occur. Therefore, the current density during plating is 0.1 A / dm ^{2 to} 8 A / excluding the reversal current of the PR current described later. dm ² is desirable. As the current density increases, poor appearance of the copper electroplated layer occurs.

In order to obtain the flexible wiring board according to the present invention, the flexible wiring board is formed using a periodic reverse current (hereinafter, sometimes referred to as a PR current) within a range of 10% or more from the surface of the copper electroplating layer serving as the wiring. .
When a PR current is used, a current that is 1 to 9 times the positive current is preferably added as the reverse current.
The switching current time ratio is preferably about 1 to 10%.
Further, the cycle of the inversion current next to the PR current flows is preferably 10 ms or more, and more preferably 20 ms to 300 ms.
FIG. 4 schematically shows the PR current time and current density.
The plating voltage may be appropriately adjusted so that the above-described current density can be realized.

In order to manufacture the two-layer flexible wiring substrate used in the present invention with a roll-to-roll continuous electroplating apparatus (plating apparatus 20), a PR current may be passed through one or more anodes from the downstream side of the transport path. The number of anodes through which the PR current flows depends on the ratio of the range in which the film is formed by the PR current from the surface of the copper electroplating layer to the polyimide film side. That is, the PR current flows through at least the anode 24t, and the PR current flows through the anode 24s, the anode 24r, and the anode 24q as necessary.
The PR current may be supplied to all the anodes, but the rectifier for the PR current is expensive, so that the manufacturing cost increases. Therefore, in the two-layer flexible wiring substrate according to the present invention, if a 10% film thickness is formed by a PR current from the surface of the copper electroplating layer in the polyimide direction, a folding resistance test (JIS C-5016-1994) Before and after the implementation, the difference d [(200) / (111)] in the crystal orientation ratio [(200) / (111)] of the copper layer becomes 0.03 or more, and as a result, the bending resistance test ( MIT test) can be improved.

  The reason why the copper electroplating using the PR current is desirable is that, when the current is reversed, the crystal grain size of copper in the copper electroplating layer can be increased to about 200 nm or more and the crystal grain boundaries can be reduced, so that the copper electroplating occurs at the grain boundaries. This is because the starting point of the crack can be reduced.

  In general, in copper electroplating, the deposited copper is affected by the surface of the substrate on which copper is to be plated. Can be controlled, and an effect on the breaking resistance of the copper electroplating layer can be obtained. Therefore, if 10% or more of the film thickness from the surface of the copper electroplating layer of the two-layer flexible wiring substrate is a crystal that matches the breaking resistance, the effect on the breaking resistance of the copper electroplating layer can be obtained. Thus, the object of the present invention can be achieved.

(4) Features of Copper Electroplating Layer The feature of the copper electroplating layer mainly constituting the copper layer in the flexible wiring board of the present invention is that it exhibits a (111) crystal orientation index of copper of 1.2 or more.
In this state, in the MIT bending resistance test (JIS C-5016-1994), the crystal becomes slippery. In addition, the copper layer of the flexible wiring board used in the present invention includes (200), (220), and (311) orientations in addition to the (111) orientation. The degree index indicates 1.20 or more.

A further feature is that the difference d [(200) / (111)] of the crystal orientation ratio [(200) / (111)] before and after the MIT bending resistance test (JIS C-5016-1994) is 0.03 or more. Is to be in a crystalline state. In this state, it is considered that the crystal slipped due to the MIT bending resistance test and recrystallization occurred.
The glossiness of the surface is preferably a glossy film so that the unevenness of the surface does not cause the notch.

The larger the average crystal grain size is, the better. However, it is necessary to pay attention to the influence on the etching of the copper layer when the copper-clad laminate is processed into a flexible wiring board by the subtractive method.
When using an aqueous ferric chloride solution for etching the copper layer in the subtractive method, the crystal grain size of the copper layer may not be affected, but when etching the grain boundaries of the crystal grains of the copper layer, The crystal grain size also affects the shape of the wiring. The average crystal grain size is desirably about 200 to 400 nm.
When the average crystal grain size is 200 nm or less, there are many crystal grain boundaries, and cracks, which are the starting points of fracture, tend to be formed. The reason for 400 nm or less is to maintain the smoothness of the metal surface.

  Further, it is necessary to reduce the surface roughness to Ra 0.2 μm or less so as not to cause a crack which is a starting point of fracture.

  That is, the copper layer of the flexible wiring board of the present invention is obtained by the above-described method for forming a copper layer, has a (111) crystal orientation index of 1.2 or more, and has a crystal orientation ratio [(200) before and after the MIT breaking test. ) / (111)], which results in a copper layer having the characteristic that the difference d [(200) / (111)] is 0.03 or more. The crystal orientation of the copper electroplated layer can be known from Wilson's orientation index of X-ray diffraction.

Furthermore, the copper crystal of the copper layer obtained by the above method has a dynamic recrystallization effect at room temperature during refraction. The average crystal grain size after the breaking resistance test tends to be about 100 nm to 200 nm by recrystallization.
Generally, it has been considered that a film formed by electroplating copper does not dynamically recrystallize at room temperature. However, the flexible wiring board of the present invention dynamically recrystallizes at room temperature, and as a result, it is difficult to cut the sample when a refraction test such as the MIT test is performed. The average crystal grain size of the copper layer and the dynamic recrystallization at room temperature can be observed in a cross-sectional SIM image.

(5) Flexible Wiring Board The result of the MIT bending resistance test of the flexible wiring board becomes worse as the wiring width becomes smaller.
That is, in the bending resistance test according to “JIS C-5016-1994”, the wiring width is 1 mm, but in the flexible wiring board used for the bent wiring in the liquid crystal display, the wiring width is 50 μm or less. The line width has shifted to a finer wiring width of 25 μm or less. Even if a flexible wiring board that is processed into a flexible wiring board with a wiring width of 1 mm for testing and can achieve sufficient breaking resistance is not enough, a flexible wiring board having a wiring width of 50 μm or less that is actually used has sufficient resistance. Sometimes breakability cannot be achieved.
Of course, in the case of a flexible wiring board having insufficient wiring resistance when the wiring width is 1 mm, even if the wiring width is set to 50 μm or less, insufficient bending resistance results.

  Furthermore, it was confirmed that by appropriately setting the cross-sectional shape of the wiring portion of the flexible wiring board, the breaking resistance was improved. Therefore, in the flexible wiring board according to the present invention, the relationship shown in the following expression (1) is required for the bottom width B, the top width T, and the width M of the bottom and the top in the cross-sectional shape in the width direction.

  When the center width M is smaller than the bottom width B and the top width T (B, T> M), cracks easily occur in the wiring due to the stress at the time of the bending resistance test, and the bending resistance is insufficient. Become. The cross-sectional shape in which the center width M is smaller than the bottom width B and the top width T is a shape in which the center is narrowed. The same applies to the case where the center width M is wider than the bottom width B and the top width T (B, T <M).

When the bottom width B is smaller than the top width T (B <T), the same cracking problem of the stress at the time of the breaking resistance test occurs, and the contact surface between the wiring and the resin film substrate becomes narrow, and the wiring This leads to a decrease in adhesion.
Here, the central part width M is the wiring width at substantially the center of the wiring thickness.

Further, it is desirable that the following formula (2) be established among the bottom width B , the center width M , the top width T, the thickness C of the copper layer, and the wiring factor F.

  When the wiring factor F is 5 or more, the top width T becomes a value close to the bottom width B, so that a crack due to stress in the bending resistance test is less likely to be formed. If the wiring factor is less than 5, the cross-sectional shape of the wiring pattern may be unsuitable for narrow pitch wiring in which the bottom is wide and the width of the top is narrow and the bottom is wide.

  In other words, the pitch of the wiring patterns (the distance between the centers of the wirings) needs to be secured for the spacing between the wiring patterns to ensure the insulation property between the adjacent wiring patterns, and also to consider the width of the bottom of the cross section of the wiring pattern. If the cross-sectional shape of the wiring pattern is flared at the bottom, the width of the bottom is taken into consideration, and thus it is not suitable for narrowing the pitch.

The formation of the cross-sectional shape of the wiring portion of the flexible wiring board that satisfies the above formula (1) can be handled by the method of manufacturing the flexible wiring board.
When wiring the above-mentioned two-layer flexible wiring substrate using a subtractive method, it can be dealt with by appropriately setting etching conditions at the time of forming a wiring portion.
For example, optimizing the shower condition of the etchant can be mentioned. Furthermore, commercially available ferric chloride and ferric chloride which are different from a typical ferric chloride aqueous solution having a specific gravity of 1.30 to 1.45 or a cupric chloride aqueous solution having a specific gravity of 1.30 to 1.45. The use of an etching solution containing dicopper and copper sulfate may be used.

Further, if the wiring is processed by the subtractive method, the cross-sectional shape of the wiring can satisfy the above equation (1) even if the crystal state of the two-layer flexible wiring substrate is controlled.
For example, since the cross-sectional shape of the wiring satisfies the above formula (1), the flexible wiring substrate 6 has an electron beam backscatter diffraction in a thickness range from the surface of the resin film substrate 1 to 0.4 μm of the metal laminate 7. The ratio (OR ₁₁₁ / OR ₀₀₁ ) of the crystal ratio OR _{111 in the} 111 direction to the crystal ratio OR _{001 in} the 001 direction of the crystal measured by the method (EBSD) can be 7 or less.

When the ratio (OR ₁₁₁ / OR ₀₀₁ ) of the crystal ratio OR _{111 in the} 111 direction to the crystal ratio OR _{001 in} the 001 direction of the crystal exceeds 7, the bottom width B, the top width T, and the height of the cross-sectional shape of the wiring pattern are increased. The wiring factor obtained from C by the following equation (3) is less than 5.

Therefore, in order to the ratio of the crystal fraction _{OR 111} of 111 orientation with respect to the crystal fraction _{OR 001 (OR 111 / OR 001} ) is 7 or less, the sputtering atmosphere during sputtering the base metal and copper in the resin film substrate, the As an example, a mixed gas of argon and nitrogen is used, and the compounding ratio of nitrogen is desirably 1% by volume or more and 12% by volume or less. Please note that there is.

When the sputtering atmosphere is only argon, the (111) plane of the face-centered cubic lattice structure can be seen in the Wilson orientation index of the crystal by X-ray diffraction of the copper thin film layer, but the (200) plane of the face-centered cubic lattice and the EBSD Little or no surface corresponding to the 001 orientation is observed.
Therefore, when nitrogen is added to argon in a sputtering atmosphere, a (200) plane of a face-centered cubic lattice is observed in the copper thin film layer, and a plane corresponding to the 001 orientation in EBSD is observed.
Under such conditions and the conditions of electroplating described later, a flexible wiring board according to the present invention in which the difference in width between the top and bottom of the wiring is small can be realized.

  Further, when the mixing ratio of nitrogen of the mixed gas of argon and nitrogen exceeds 12% by volume, when the obtained metal laminate is used for wiring such as a flexible wiring board, the heat resistance of the wiring may be reduced. , Undesirable.

The sputtering atmosphere may be appropriately examined while confirming the ratio of the crystal ratio OR _{111 in} the 111 direction to the crystal ratio OR _{001 in} the 001 direction of the metallized resin film crystal obtained by performing the final electroplating on the resin film substrate. . Note that an example of a sputtering atmosphere using an argon / nitrogen mixed gas is shown; however, the sputtering atmosphere is not limited to an argon / nitrogen mixed gas as long as a desired crystal state can be achieved.

Further, it is desirable to optimize the sputtering conditions, and further optimize the copper electroplating conditions. As the conditions, the atmosphere for the sputter deposition of the base metal layer and the copper thin film layer during the production of the two-layer flexible wiring board, A current density of 1 A / dm ² is used in a range of 1 μm to 2.5 μm in thickness from the surface of the copper thin film layer of the copper electroplating layer using an argon / nitrogen mixed gas containing 1% to 12% by volume of nitrogen. Film forming method.

  Further, even if the resin film substrate provided with the metal laminate as the wiring is etched, the orientation ratio of the crystal in the thickness range of 0.4 μm from the resin film substrate surface of the wiring does not change.

The present invention has been described so far mainly on the method of obtaining the flexible wiring board according to the present invention by the subtractive method.
To obtain the flexible wiring board according to the present invention by the semi-additive method, when copper electroplating on the two-layer flexible wiring board, it is also possible to take the same copper plating procedure as the above-described two-layer flexible wiring board, The thickness of the copper layer may be appropriately determined in consideration of the thickness of the copper plating of the semi-additive method.

The thickness of the copper layer constituting the wiring portion of the flexible wiring board is desirably 5 μm to 12 μm.
When the thickness of the copper layer is less than 5 μm, the conductivity of the wiring becomes insufficient. On the other hand, if the copper layer exceeds 12 μm, it is difficult to form a wiring having a wiring width of 50 μm or less even if the conductivity is sufficient. In particular, in the subtractive method, as the thickness of the wiring increases, it becomes more difficult to process fine wiring.
The total thickness of both the copper thin film layer and the copper electroplating layer of the two-layer flexible wiring board (corresponding to the thickness of the copper layer of the flexible wiring board) may exceed 12 μm. As described above, when the total thickness of the copper thin film layer and the copper electroplating layer of the two-layer flexible wiring substrate exceeds 12 μm, the copper electroplating layer of the two-layer flexible wiring substrate is subjected to a predetermined film by chemical polishing or the like. It is sufficient that the crystal structure of the copper layer of the flexible wiring board according to the present invention can be maintained after the film thickness has reached a predetermined value.

On the surface of the wiring, tin plating, nickel plating, gold plating, or the like is applied as necessary to a necessary portion by a known plating method, and the surface is covered with a known solder resist or the like. Then, electronic components such as semiconductor elements are mounted to form an electronic device.
More specifically, the processed flexible wiring board is coated with a known solder resist and mounted with elements such as ICs via gold bumps after being subjected to tin plating. Processed into
In the flexible wiring board according to the present invention, conditions such as copper electroplating and processing into IC package parts are performed so that a characteristic crystal structure can be maintained even after a process such as tin plating, solder resist coating or IC mounting. Conditions may be appropriately selected.

Hereinafter, the present invention will be described in more detail with reference to Examples.
A polyimide film with a copper thin film layer using a polyimide film for the resin film substrate was manufactured using a roll-to-roll sputtering apparatus 10 shown in FIG.
A nickel-20% by weight chromium alloy target for forming a base metal layer is mounted on the sputtering cathode 15a, and a copper target is mounted on each of the sputtering cathodes 15b to 15d. A 38 μm thick polyimide film (Kapton: registered trademark) is mounted on a resin film substrate. (Made by Toray DuPont) was evacuated, and the inside of the device was kept at 1.3 Pa to produce a polyimide film with a copper thin film layer. The thickness of the underlying metal layer (nickel-chromium alloy) was 20 nm, and the thickness of the copper thin film layer was 200 nm.

  Copper electroplating was performed on the obtained polyimide film with a copper thin film layer using a plating apparatus 20 to form a copper electroplating layer. As the plating solution, an aqueous solution of copper sulfate having a pH of 1 or less is used, and the anodes 24m to 24t have the maximum current density (excluding the reversal current of the PR current) unless otherwise specified. The current density was adjusted to 8.5 μm.

The bending resistance test was performed by a subtractive method using ferric chloride as an etchant to form a test pattern of "JIS C-5016-1994", and evaluated according to the same standard, and set the wiring width to 20 μm. Other than the above, the evaluation was performed according to “JIS C-5016-1994”.
The crystal orientation of the copper electroplated layer before and after the bending resistance test was measured by Wilson's orientation index by X-ray diffraction.

  In order to perform electroplating using a PR current from the surface of the copper electroplating layer to a thickness range of 10% using a sputtering atmosphere of argon gas from the surface of the copper electroplating layer, a PR current was passed through the anode 24t, and the two-layer flexible wiring of Example 1 was used. A substrate was prepared. The negative current time ratio at this time was set to 10%.

  Using a subtractive method, a two-layer flexible wiring board prepared for evaluating the bending resistance of the flexible wiring board was subjected to a subtractive method to form a test pattern (wiring width 1 mm) of "JIS C-5016-1994" and a wiring width. A flexible wiring board according to Example 1 was manufactured by forming a wiring of 20 μm, and was evaluated according to “JIS C-5016-1994”.

The difference in the crystal orientation ratio [(200) / (111)] expressed by the X-ray orientation index before and after the MIT breaking resistance test was 0.04.
In the MIT bending resistance test, favorable results were obtained: 851 times with a wiring width of 1 mm and 45 times with a wiring width of 20 μm.
Wiring factor _{F E} of the wiring width 20μm was 5.5.
The bottom width (B) was 20.0 μm, the intermediate width (M) was 18.5 μm, and the top width (T) was 16.9 μm.

The sputtering atmosphere was a mixed gas of 1.3 Pa of argon and 5% by volume of nitrogen.
In the copper electroplating layer, the current density of the anodes 24a to 24f for forming a film having a thickness of 1.5 μm from the surface of the copper thin film layer in the copper layer is set to 1 A / dm ² or less, and 10% In order to perform electroplating using the PR current up to the film thickness range of, a PR current was passed through the anode 24t to produce a two-layer flexible wiring substrate according to the second embodiment. The negative current time ratio at this time was set to 10%.

  The difference d [(200) / (111)] of the crystal orientation ratio [(200) / (111)] expressed by the X-ray orientation index before and after the MIT breaking resistance test was 0.04.

In the MIT bending resistance test, the printed wiring board according to Example 2 exhibiting the above characteristics exhibited good results of 545 times when the wiring width was 1 mm and 50 times when the wiring width was 20 μm.
Wiring factor _{F E} of the wiring width 20μm was 6.3.
The bottom width (B) was 20.0 μm, the intermediate width (M) was 18.7 μm, and the top width (T) was 17.3 μm.

(Comparative Example 1)
The test piece according to Comparative Example 1 having a wiring width of 20 μm was prepared by increasing the pressure of the shower of the etchant for the two-layer flexible wiring substrate of Example 1.
The folding resistance of the printed wiring board according to Comparative Example 1 having the above characteristics showed a result of not swinging 20 times at a wiring width of 20 μm, which was clearly inferior to Example 1 according to the present invention.
The bottom width (B) was 20.0 μm, the middle width (M) was 16.4 μm, and the top width (T) was 17.1 μm.

In the embodiment of the wiring width 20μm in Table 1, are summarized wiring shape (bottom width B, the intermediate width M, top width T, copper film thickness C) and the sputtering atmosphere, and the calculated wiring factor F _E.

1 polyimide film (resin film substrate)
2 base metal layer 3 copper thin film layer 4 copper electroplating layer 5 copper layer 6 two-layer flexible wiring board 7 metal laminate 10 roll-to-roll sputtering device 12 housing 13 unwind roll 14 can rolls 15a, 15b, 15c , 15d Sputtering cathode 16a Front feed roll 16b Rear feed roll 17a, 17b Tension roll 17b Tension roll 18 Winding roll 20 (Roll-to-roll continuous electro) plating apparatus 21 Electroplating tank 22 Unwinding roll 23 Inverting rolls 24a to 24t Anode anodes 26a to 26k Power supply roll 28 Plating solution 28a Plating solution level 29 Winding roll F Polyimide film (resin film substrate)
F2 Polyimide film with copper thin film layer S Substrate for 2-layer flexible wiring

Claims (4)

On a surface of the resin film substrate, a flexible wiring board provided with a wiring of a metal laminate composed of a base metal layer made of a nickel alloy and a copper layer provided on the surface of the base metal layer without using an adhesive,
The ratio of [(200) / (111)] orientation of the crystal orientation ratio of the copper layer obtained before and after the execution of the “bending resistance test specified in JIS C-5016-1994” is obtained by the wiring of the metal laminate. The difference d [(200) / (111)] is 0.03 or more,
The crystal ratio OR _{111 in the} 111 direction with respect to the crystal ratio OR _{001 in} the 001 direction of the crystal measured by electron beam back scattering diffraction (EBSD) in the thickness range of 0.4 μm from the surface of the resin film substrate to the metal laminate. (OR ₁₁₁ / OR ₀₀₁ ) is 7 or less,
When the bottom width B and the top width T of the cross-sectional shape in the width direction, and the center width M at the center of the bottom and the top substantially have the following formula (1), and the bottom width B is 50 μm or less,
The flexible wiring board , wherein the bottom width B , the center width M , the top width T, and the thickness C of the copper layer have a relationship represented by the following expression (2).

  The flexible wiring board according to claim 1, wherein the thickness of the base metal layer is 3 nm to 50 nm.   The flexible wiring board according to claim 1, wherein the copper layer has a thickness of 5 μm to 12 μm.   The resin film substrate is at least one resin selected from a polyimide film, a polyamide film, a polyester film, a polytetrafluoroethylene film, a polyphenylene sulfide film, a polyethylene naphthalate film, and a liquid crystal polymer film. The flexible wiring board according to any one of claims 1 to 3, wherein the flexible wiring board is a film.

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